Adrenoleukodystrophy (ALD) is an X-linked genetically determined disorder that affects the nervous system white matter and the adrenal cortex. Its clinical course is highly variable. The childhood cerebral form is the most severe phenotype, which affects approximately 35% of patients with the ALD gene defect. Patients with this phenotype develop cognitive and neurologic deficits before age 10 years, and become totally disabled within two years. The principal biochemical abnormality is the abnormally high level in plasma and tissues of saturated very long chain fatty acids (VLCFA) due to the impaired capacity to degrade these substances. The oral administration of glycerol trierucate (GTE) has been shown to normalize plasma VLCFA levels within 4 weeks. The question being investigated is whether administration of GTE to neurologically asymptomatic ALD patients can reduce the frequency and severity of subsequent neurologic disability.